Metal Storm seems to have been around forever. I can dimly
remember the first publicity clips of a box-like device firing pistol-calibre
ammunition at "a million rounds per minute", and wondering what use it could be.
In fact, I recall describing it several years ago as "a solution in search of a
problem". However, it has evolved considerably in recent years and is worth
another look.

For those unfamiliar with the Metal Storm (MS)
concept, it involves stacking several rounds of ammunition in line in one gun
barrel, and firing them electrically in sequence (from the front backwards,
obviously!). This provides multiple shots from a single-barrel weapon without
the complexity, weight, size and potential unreliability of an autoloading
system. Such stacked ammunition is not a new idea, being tried in the old
gunpowder days, but poor gas seals between the rounds of ammunition led to a
tendency for the whole stack to go off at once. The invention of the metallic
cartridge case put paid to such experiments since stacked rounds, by definition,
have to be caseless. The modern caseless propellant and gas seals developed by
Metal Storm are clearly secure, and the electrical firing system much simpler
than the earlier efforts. It has been exhaustively tested by several military
organisations and appears to be a technical success, although it has so far not
entered service. Perhaps because the question still remains: what's it good for?

All manner of different MS weapons have been
proposed although, ironically, few of them make use of the vaunted high rate of
fire, one exception being a naval CIWS (close-in weapon system). Other
suggestions have ranged from a rapid mine-scattering device to a pistol. But the
current marketing emphasis is, far more realistically in my view, on grenade
launchers. I say realistically because the characteristics of the MS system are
best suited to short, fat, low-velocity ammunition. One of the main constraints
of the system is on barrel length; the more rounds are stacked, the more of the
barrel they use up and the greater the difference in the barrel length travelled
by the first and last projectiles. High-velocity rifle or cannon ammunition need
a lot of propellant so their rounds are very long for their calibre, meaning
that you can get very few of them in a barrel. Furthermore, they generate very
high gas pressure, which would stress the gas seals more. So the grenade rounds
are an appropriate choice.

Metal Storm has teamed up with Singapore
Technologies Kinetics (STK), one of the world's most prolific developers and
manufacturers of 40mm grenade ammunition. The MS rounds basically use STK
projectiles with a caseless propellant and gas seal unit fixed to the back in
place of the usual cartridge case. The principal marketing focus is on low
velocity (LV) rounds said to match the performance of the conventional LV
ammunition (muzzle velocity 76 m/s, maximum range 400m), with three different
weapons developed to use them: FireStorm, Redback and the 3GL.

FireStorm is a light vehicle-mounted system which
combines four barrels, each holding four rounds. The mounting is intended to be
installed on top of a vehicle and fired remotely from within, to provide
close-in defence. I have to say I am dubious about this. Lightweight belt-fed
automatic grenade launchers (AGLs) are available which fire far more effective
40mm high velocity (HV) ammunition and these don't run out of ammo after only
sixteen rounds. Redback is a more sophisticated version of the same thing,
designed to be an element in a vehicle's active defence system against incoming
missiles when coupled to a very sophisticated detection and fire control suite.
Here the high rate of fire is useful.

The 3GL seems to me to have more interesting
possibilities. This is a single-barrel three-round unit which can either be
fitted with a stock as a stand-alone weapon or attached to a rifle as a
replacement for the very common single-shot underbarrel grenade launchers (UGLs).
No weights or measurements have been provided so far (the MS website and
publicity material are singularly uninformative when it comes to technical data)
but although the 3GL is said to be light, it is clearly quite long, which is not
handy if you wish to attach it to a carbine or, especially, a bullpup. It does
provide three shots in a small fraction of the time it would take to load, aim
and fire a standard UGL three times, which could be very useful in certain
circumstances, such as ambushes (in both attack and defence). And it is
unquestionably much lighter and more compact than a conventional three-round
repeating launcher would be.

The first stage of development of the MS concept involved
stacked rounds clipped together into modules at the factory, in which the
propellant could be adjusted slightly for each round to equalise the muzzle
velocities. Clipped stacks are still available, but they are not ideal for the
3GL – soldiers need to be able to "top up" their ammunition in the field, and to
reload quickly and conveniently. The 3GL therefore can also be used with
individually-loaded rounds – the barrel slides forwards to permit breech loading
– which means that they all must have the same propellant loads. This is
apparently acceptable, as the difference in muzzle velocity between the first
and last rounds is said to be small.

So far so good – but I think that this concept could be
developed further, to provide a primary rather than auxiliary weapon for some
soldiers. The changes I envisage being needed to achieve this go in the
following sequence:

1.Design
a stand-alone shoulder gun without considering any UGL applications.

2.Switch
from the LV to the new medium-velocity (MV) rounds (which MS is already working
on). These double the maximum range to 800m, but more importantly halve the
trajectory height and projectile flight time to any range, providing far greater
practical accuracy.

3.The
only downside with MV ammunition is the increased recoil, since the muzzle
velocity is raised to 105-120 m/s. It has been calculated that a weapon firing
MV ammunition should weigh at least 5 kg to reduce the recoil to a level which
the average soldier will find tolerable. A typical conventional single-barrel
40mm LV launcher, with stock, weighs around 2.5 kg, give or take a bit.

4.If
the weight needs to be doubled to cope with MV ammunition, then a virtue can be
made from necessity by giving it two barrels. This would not only double the
"magazine" capacity, it would provide the option of loading each barrel with
different ammunition – say, HE in one barrel, shot or flechette rounds in the
other for close-quarter fighting – with the choice between them being made at
the flick of a switch.

5.Since
there is no need to provide space for a reloading mechanism, there is no reason
to provide a conventional stock or even a receiver. The weapon could simply
consist of the two barrels (stacked one above the other), a combined breech
mechanism and very short butt attached to the back end, and a skeleton framework
clamped to the barrel, supporting Picatinny rails. The breech block could flip
open sideways to permit reloading (and incidentally, unlike the 3GL, there would
be no restriction on the length of the rounds which could be loaded). The back
of the breechblock, which forms the butt, could either be thickly padded or if
necessary fitted with an hydraulic recoil damper. This layout would save the
weight of the stock and allow the barrels to be significantly longer while
keeping the overall length of the weapon short. This would provide space for
more than three rounds per barrel – at least four, and possibly up to six
depending on weight considerations and possibly on the acceptable degree of
variation in muzzle velocity.

6.Some
other details: the Picatinny rails would include electrical contacts. This would
mean that the pistol grip unit – which would include the trigger, safety, barrel
selector and battery – could be attached anywhere on the underside rail to
adjust the length of pull to the user's choice. The location of the forward
handgrip/bipod, sights and cheek-piece could be similarly adjusted. The
electrical contacts would also facilitate the addition of STK's air-burst
system, using fuze setters on the muzzle.

7.Safety concerns about having the breech so
close to the firer's head could be addressed not only by safety interlocks to
prevent the gun from being fired unless the breech is securely locked, but also
by fitting a Kevlar shield.

The potential advantages of such a weapon appear to be
considerable. Compared with the obvious rivals – the six-shot revolver GLs – it
would be far more compact, much faster-firing, have a larger ammunition capacity
and would offer the instant availability of two different ammunition types. A
tactical option, depending on the circumstances, could be to keep one barrel
loaded and leave the other free to single-load specialised rounds such as flare,
smoke, or video reconnaissance types. With the STK grenade range to choose from,
it would be very cheap to pick any existing projectiles (including less-lethal
types for riot control) and attach the MS propellant/gas seal unit to them. The
use of shot projectiles – or the development of multiple flechette loadings –
would provide a devastating close-quarter battle capability which, with at least
eight rounds available, could make the carrying of a second weapon unnecessary.
A heavy single-flechette round could also provide a useful long-range
performance against body armour.

It could not replace the military rifle – each weapon has its
pros and cons – but it could take its place alongside it as a very versatile
addition to the infantryman's armoury.

In 2012 the original
Australian Metal Storm company went into receivership. However, the US
branch continues in operation and the Canadian Army is incorporating an
integrated MS grenade launcher in its planning for future assault
rifles. The Metal Storm website is HERE.